Manufacture of articles by drawing and blow-moulding

ABSTRACT

A process for the manufacture of articles from a thermoplastic of polyester or polyamide type, preferably of polyethylene terephthalate, the element consisting of an edge part which surrounds a body in an arrangement in which the latter is sunk relative to the edge part. The element is formed from a blank of mainly amorphous material or from a material having a crystallinity of less than 10%. The blank consists, for example, of a flat plate, a blank shell or the like. The body or parts thereof are shaped by stretching the blank until that material flows which is located within the material sections of the blank, which form the edge part in the element, the material stretched up to flowing in the body assuming a crystallinity of between 10% and 25%, while the crystallinity in the material in the edge part and in the unstretched parts retains its original value of less than 10%. At least the body of the element is expanded against warm mould walls until the final shape of the particular article is obtained. Optionally, the expansion is preceded by a number of drawing steps with an axial elongation of the body coupled with a simultaneous reduction in its dimensions at right angles thereto.

BACKGROUND OF THE INVENTION

The invention relates to the manufacture of articles from athermoplastic of polyester or polyamide type, preferably of polyethyleneterephthalate, the articles being formed from an element which consistsof an edge part which surrounds a body in an arrangement in which thelatter is sunk relative to the edge part. The element is formed from ablank of mainly amorphous material or from a material having acrystallinity of less than 10%. The blank consists, for example, of aflat plate, a blank shell or the like. The body or parts thereof areshaped by stretching the blank until that material flows which islocated within the material sections of the blank, which form the edgepart in the element, the material stretched up to flowing in the bodyassuming a crystallinity of between 10% and 25%, whilst thecrystallinity in the material in the edge part and in the unstretchedparts retains its original value of less than 10%. The edge part issevered from the body, the latter being elongated in the axial directionby a number of drawing steps, whilst the dimensions of the body at rightangles thereto are reduced at the same time. The body of the element ofthe drawn part is reshaped by a blow-moulding process to give thearticle.

In the manufacture of products from thermoplastics, the startingmaterial is in most cases a virtually flat blank. Either an end productis formed here substantially in one deformation step, or a premouldingis formed for later reshaping to give the end product. The shaping ofthe blank is effected, according to methods known at present, either bythe blow-moulding process or by the thermo-forming process. In theblow-moulding process, thick sections are as a rule obtained in thebottom. In the thermo-forming process, either so-called negativethermo-forming or so-called positive thermo-forming is used. In thenegative thermo-forming process, a thin bottom is obtained, whilst athick bottom is obtained in the positive thermo-forming process.

In negative thermo-forming, a warm sheet or a warm film is placed overcavities, after which the material of the film or the sheet is pressedand sucked into the cavities by external pressure and internal reducedpressure. This has the result that the material is stretched and becomesthin, when it is sucked into the particular cavities. If the cavity is acup, a thin stretched bottom and a wall thickness increasing in thedirection of the edge of the cup are obtained.

In positive thermo-forming the cup mould forms a projecting body and thematerial of the film or sheet is pressed and sucked over this projectingbody. This has the result that the material on the upper part of theprojecting body, that is to say the bottom of the cup, remains thick andessentially unstretched, whilst the thickness of the material decreasestowards the edge of the cup.

To obtain an adequate material thickness in the bottom part of the cupin negative thermo-forming, a sufficient thickness in the startingmaterial must be chosen. To obtain an adequate thickness in the edgezone of the cup by positive thermo-forming, which is necessary forstability of the cup, a sufficient thickness of starting material mustlikewise be chosen. In negative thermo-forming, the material zonesbetween the shaped cups remain uninfluenced and are subsequentlysevered, after the manufacture of the actual cups. In positivethermo-forming, the material between the cups is drawn into recesses andsevered from the cups formed. In positive thermo-forming, cup bottomsare thus obtained which have substantially the same thickness as thestarting material. Both forming processes require an unnecessarily highconsumption of material, which is of economic importance in the massproduction of articles.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method whicheliminates certain disadvantages connected with the technology hithertoknown.

The invention is suitable preferably for the manufacture of articlesfrom thermoplastics of the polyester or polyamide type. Examples of suchmaterials are polyethylene terephthalate, polyhexamethyleneadipamide,polycaprolactam, polyhexamethylene-sebacamide, polyethylene 2,6- and1,5-naphthalate, polytetramethylene 1,2-dihydroxybenzoate and copolymersof ethylene terephthalate, ethylene isophthalate and similar polymers.The description of the invention below relates mainly to polyethyleneterephthalate, called PET in the further text, but the invention is notrestricted exclusively to the use of either this material or othermaterials already mentioned; instead, it is also suitable for many otherthermoplastics.

For a better understanding of the existing problem and of the invention,several characteristic properties of the polyester polyethyleneterephthalate are described below. From the literature, for exampleProperties of Polymers, by D. W. van Krevelen, Elsevier ScientificPublishing Company, 1976, it is known that the properties of thematerial change when amorphous polyethylene terephthalate is oriented.Some of these changes are shown in the diagrams, FIGS. 14.3 and 14.4 onpages 317 and 319 in the book "Properties of Polymers". The symbols usedin the discussion below correspond to the symbols in the said book.

PET, like many other thermoplastics, can be oriented by stretching thematerial. Normally this stretching takes place at a temperature abovethe glass transition temperature Tg of the material. The strengthproperties of the material are improved by orienting. The literatureshows that, in the case of the thermoplastic PET, an increase in thestretching ratio Λ, that is to say the ratio of the length of thestretched material and the length of the unstretched material, alsoleads to an increase in the improvement of the material properties. Whenthe stretching ratio Λ is increased from about 2 to a little more than3, particularly large changes in the material properties are obtained.The strength in the direction of orientation is here markedly improved,whilst at the same time the density ρ and likewise the crystallinity Xcrises and the glass transition temperature Tg is raised. It can be seenfrom the diagram on page 317 that, after stretching, with Λ assuming thevalue of 3.1, the material withstands a force per unit area, whichcorresponds to σ=10, coupled with a very small elongation, whilst theelongation at Λ=2.8 is substantially larger. In the further test, theterm "step" is sometimes used to designate orienting which is obtainedby stretching, or a reduction in thickness by at least about 3 times,and which leads to the marked improvements of the material properties,indicated above.

The diagrams quoted above show changes which are obtained on mono-axialorientation of the material. In biaxial orientation, similar effects areobtained in both directions of orientation. Orientation is carried outas a rule by successive stretchings.

Improved material properties, corresponding to those which are obtainedby the "step" defined above, are also obtained if an amorphous materialis stretched until it flows and, before flowing, the material is at atemperature which is below the glass transition temperature Tg. In a rodbeing drawn, a reduction of the diameter of about 3 times results in theflow zone. On drawing, the flow zone is continuously displaced into theamorphous material, whilst at the same time the material, which hasalready undergone the state of flowing, absorbs the tensile forces ofthe test rod without an additional permanent stretching.

According to the invention, an element is produced which consists of anedge part and a cup part, starting from a substantially flat blank ofamorphous material or having a crystallinity of less than 10%. Thematerial in annular sections in the blank is transformed into the stateof flow by a drawing process. The cup part is formed in this way. Incertain applications, the ratio between the radial and the axialexpansion of the cup is such that production of the beaker in a singledrawing step is not possible. According to the invention, the desiredratios are obtained by a number of redrawing steps of the cup, thediameter of the cup being reduced in each redrawing step, whilst thethickness of the material remains more or less unchanged.

The cup part of the element or the drawn cup is reshaped by ablow-moulding process to give the article.

According to the invention, an element is obtained which consists of anedge part and a cup part, the material preferably being of more or lessuniform thickness and orientation in the entire bottom of the cup part(cup). In a certain embodiment of the invention, the material in thebottom part of the cup moreover consists completely or partially ofmaterial of the same thickness as that of the material of the wall. Theremaining sections of material have the thickness and materialproperties of the material. In certain applications, the bottom is moreor less completely flat, whilst in other applications the bottomconsists of parts which are axially displaced relative to the axis ofthe cup. In this case, in certain embodiments, annular edge sections areformed adjoining the lower edge of the wall, whilst in other embodimentscentral bottom sections are displaced further away from the upperopening edge of the element.

The element consists of an edge part which surrounds a body which issunk relative to the edge part. The material in the edge part is mainlyamorphous or has a crystallinity of less than 10%. The body has a wallpart and a bottom part. The wall part consists of material which hasbeen drawn at a temperature below the glass transition temperature Tg,until flow sets in, and in which the crystallinity is between 10% and25%. In the basic design of the element, the bottom consists of mainlyamorphous material or of material having a crystallinity of less than10%. In embodiments of the invention, the bottom consists, as desired,of material which has been drawn at a temperature below the glasstransition temperature Tg and at a crystallinity between 10% and 25%,until flow sets in, that is to say of a material having properties whichmainly are identical to the material properties of the wall part of theelement, or of material sections which have been drawn until flow setsin and which alternate with material sections of mainly amorphousmaterial or material having a crystallinity of less than 10%. In certainembodiments, the material zones already mentioned are displaced in theaxial direction relative to the lower edge of the wall part.

During the production of an element, a mainly flat blank ofthermoplastic, having a crystallinity of less than 10%, is clamped in ata temperature below the glass transition temperature Tg betweencounter-holders, so that a zone is formed which is completely surroundedby the clamped-in material sections. A press device the contact surfaceof which is smaller than the surface area of the zone, is appliedagainst this zone. Thus, a closed strip-like material zone is formedbetween the clamped-in material sections of the blank and that part ofthe zone which is in contact with the press device. Subsequently, adrive mechanism shifts the press device relative to the counter-holder,while the press device remains in contact with the zone. The material inthe strip-like zone is thus stretched in such a way that flow of thematerial occurs, the material being monoaxially oriented, whilst at thesame time the thickness of the material is reduced by about 3 times inthe case of PET. The wall part of the element is formed during thestretching process.

Since the circumference of the contact surface of the press device issmaller than the inner circumference of the clamping devices, thematerial which adjoins the edge of the press device is subjected to thegreatest stress, for which reason the flow of the material normallystarts at this point. The effect thus resulting is further reinforced bythe fact that the transition from the contact surface of the pressdevice to the side walls of the press device is made relativelysharp-edged. When flow has set in, the zone of flow of the material isgradually shifted in the direction of the clamping devices. In certainapplication examples, the press step is interrupted when the flow zonehas reached the press devices. In other application examples, the pressstep continues, renewed flowing of the material taking place adjoiningthe edges of the press device and being displaced from these zonestowards the center of the material. When all the material which is incontact with the contact surface of the press device has undergone flow,that material between the clamping devices which is located next to theinner circumference of the clamping devices is utilized for a furtherdrawing step in certain application examples. To make this possible, asomewhat elevated temperature in this material is normally required. Thestarting temperature, however, is still below the glass transitiontemperature Tg.

In certain application examples, accelerated cooling of the drawnmaterial is necessary. In this case, the press device is preferablyprovided with a cooling device which is arranged in such a way that thezones of the material, which flow during drawing of the material, are incontact with the cooling device.

In certain applications, the flow of the material is caused to startadjoining the clamping devices. This is accomplished by providing theclamping devices with heating devices which raise the temperature ofthose material sections where flow is to start. The temperature in thematerial, however, is still below the glass transition temperature Tg ofthe material. When flow has set in, this continues in the direction ofthe contact surface of the press device and, in some cases which mayoccur, it continues past the transition from the side walls to thecontact surface of the press device. To ensure that the clamping devicesretain the blank in the future edge sections of the element, theclamping devices are as a rule provided with cooling devices.

The concept of the invention also comprises the possibility that, by anumber of drawing steps which are arranged one after the other, both inthe wall part and in the bottom part of the body, material sections areobtained which alternately consist of material sections which have beendrawn until flow sets in and have in this way been given a reduced wallthickness, and undrawn material sections which have retained their wallthickness. In material sections located in the bottom part of the body,a displacement of the material in the axial direction of the body alsotakes place in certain application examples in conjunction with thedrawing step.

The edge part is removed from the element formed and the element isreshaped by a number of drawing steps. These drawing steps take place ata temperature below the glass transition temperature Tg and effect areduction of the diameter of the cup, whilst the length of the body isextended at the same time in the axial direction. The drawing stepeffects exclusively a redistribution of the material without flowsetting in.

The cup formed after the end of the drawing step has an opening at oneend, whilst it has a bottom part at the other end. Depending on themanner in which the element has been shaped, the bottom part consistswholly or partially of amorphous material or of unoriented material. Inthe first-mentioned case, the bottom part thus retains the thickness ofthe starting material in the amorphous zone or in the amorphous zones.The amorphous material is suitable for use as a fixing material forwelding additional parts to the cup. This requirement will be present,for example, when the cup is used as a container and the bottom part ofthe cup simultaneously represents the bottom part of the container. Inthis case, it is advantageous to weld an external foot to the container.The cup shaped in the manner described possesses an opening part which,if appropriate after reworking, is preferably expanded in such a waythat a beaded edge results, the stability of the beaded edge beingincreased by heating up to the maximum crystallisation temperature ofthe material. The beaded edge is thus outstandingly suitable forfitting, for example, a loose lid of a suitable material, for examplemetal, by crimping.

In another application example, the drawing step at the cup isinterrupted so that parts of the cup have a reduced diameter comparedwith the initial diameter. By removing the bottom from this part ofsmaller diameter, expanding the edge formed and stabilising the openingwhich has been formed in the manner described in the preceding section,a mouth part is obtained which is suitable for fitting, for example, aclosure or a crown cap. The other still open part of the cup is closed,for example, by an end disc, in a manner similar to that alreadydescribed.

In the blow-moulding process, the starting point is either a cup whichhas been severed in the normal way from the edge part of the element, orfrom a newly drawn cup. By blow-moulding against warm mould walls, thecup, the material of which is at a temperature above the glasstransition temperature Tg, is reshaped in such a way that it has exactlythe form of the intended end product. In certain applications, a warmblowing mandrel is used in order to prevent excessive cooling of thematerial during the blow-moulding step.

It can be seen from what has been said that the combination of drawing,until flow sets in to obtain an element, redrawing of the cup of theelement formed and a blow-moulding step offers many optionalpossibilities for the shaping of different types of articles.

An article produced in the manner described above is thus not onlysuitable for use as a container, but many applications are possible.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be described in detail with reference to thedrawings, wherein

FIGS. 1-2 show optional embodiments of bands suitable for reshaping,

FIG. 3 shows an element having a bottom part of the body, consistingmainly of amorphous material,

FIGS. 4-10 show the principles of devices for drawing of the element,

FIG. 11 shows a part of a device for redrawing of the cup of theelement,

FIG. 12 shows the cup of the element before redrawing,

FIG. 13 shows the cup of the element after partial redrawing,

FIG. 14 shows the cup of the element after complete redrawing,

FIG. 15 shows the cup of the element, having the part of the cup, whichwas partially redrawn, according to FIG. 13, after renewed redrawing,

FIG. 16 shows a container produced from a cup according to FIG. 15,

FIGS. 17-19 show the counterparts to FIGS. 12-14, the bottom part of thecup having sections of amorphous material and

FIGS. 20-22 show optional embodiments of blow-moulded articles.

DETAILED DESCRIPTION

FIGS. 1-2 show a band or a blank 14', 14" of thermoplastic, the bands orblanks being seen from above. In the figures, annular material zones16', 16" or 17', 17" are represented. Moreover, a material zone 15', 15"is indicated which is surrounded by the original annular material zone17', 17". The material zone 16 marks that zone which, on drawing of theblank, is clamped in between the clamping devices 30a-b (see FIG. 4).The material zone 15 marks that zone which, on drawing of the blank, isin contact with the press face of the press device 20 (see FIG. 4). Thematerial zone 17 marks that zone which, on drawing of the blank, isbrought into the state of flow.

An element 10 consisting of an edge part 12 of the body 13 is seen inFIG. 3. The body in turn consists of a wall part 18 and a bottom part11. In the figure, the wall part consists of drawn material of reducedthickness compared with the thickness of the starting material. Thebottom part 11 consists of material which, while retaining its materialproperties, has been displaced in the axial direction of the body.Moreover, a zone 19 is marked in which material belonging to the edgepart 12 had been transformed into the state of flow.

In FIGS. 4-8, a number of clamping devices 30a, 30b which fix the blank14 can be seen. A press device 20 having a press face 21 is locatedbetween the clamping devices 30. In FIG. 4, the press device is in aposition in which the press face 21 is located directly next to theupper surface of the blank 14. In FIG. 5, the press device was shifteddownwards, flow of the material having started from a transition zone atwhich the original thickness of the blank is reduced to the drawnthickness of the element. It is seen that the drawing takes placebetween the outer surface of the press element and the inner surface ofthe clamping devices without contact of the drawn material with thesesurfaces whereby a so-called free drawing takes place. In FIG. 6, thepress device has been shifted to such an extent that an elementaccording to FIG. 3 has been formed. In FIG. 7, the press device was yetfurther shifted, further flow of the material having taken place. Anelement 10' has thus been formed, the body 13' of which has a bottompart 11, the central sections of which consist of amorphous undrawnmaterial which is surrounded by drawn oriented material in which flowhas taken place. Finally, in FIG. 8, the press device 20 has beenshifted to such an extent that virtually the entire material in thebottom part 11" of the body 13" has undergone flow. An element 10' hasthus been formed in which both the wall part and the bottom part of thebody have a reduced wall thickness because the material has been in thestate of flow and has at the same time been oriented.

In FIGS. 9-10, an optional embodiment of the clamping devices 33a-b isrepresented, which are provided with cooling channels 31 and heatingchannels 34. In the figures, only the feedline for the heating channelsis shown, whilst the discharge line for the heating channels is locatedbehind the feedline in the figures and is indicated by theupward-pointing arrow. The cooling channels, like the heating channels,are covered by plate-like covers 35, the other surface of which at thesame time represents the contact surface of the clamping devices forclamping the blank. An insulation 32 separates the cooled zone of theclamping devices from the heated zone. In certain applications, theheating channels are used as the cooling channels in the same way.

Furthermore, the figures show an optional embodiment of a press device20a which also has cooling channels 22. The cooling channels are coveredby a cooling jacket 23 which at the same time represents the outercontact surface of the press device opposite the material during theprocess of drawing the latter. FIG. 9 shows a position of the pressdevice, which corresponds to the position shown in FIG. 5, and FIG. 10shows a position of the press device, which corresponds to the positionin FIG. 8. The press device is constructed with a face of rotationallysymmetrical curvature, which is shaped in such a way that, on drawingwithin the flow range, the material is always in contact with thecooling jacket, whilst that material which has not yet been in the stateof flow is not in contact at any point with any device in the zonebetween the press device and the clamping devices.

Heating of the material with the aid of the heating channels 34 has thepurpose of increasing the readiness of the material to flow. Heating islimited, however, in such a way that the temperature of the material isalways lower than the glass transition temperature Tg. Heating makes itpossible to allow the drawing step of the material to continue a littleinto the zone between the jaws of the clamping devices, as shown in FIG.10. Another optional application, where the increased readiness of thematerial to flow is exploited, is obtained when, during the drawingstep, the zone of initial flow of the material is directed to the zonenext to the inner edges of the clamping devices. After flow has takenplace, the flow zone is gradually displaced in the direction away fromthe clamping devices towards the bottom of the press device, as thepress device gradually shifts downwards as in the figures.

The result of this is that flow always propagates in the same direction,and a new start of flow is avoided, such as takes place when theembodiment of the invention shown in FIGS. 4-8 is used.

FIG. 11 shows a device for redrawing the element formed before. In thefigure which shows only a part of the device, a press plunger 40, acounterholder ring 41, a clamping ring 42 and a wall part 18 in theelement are seen, the wall part being in the process of shaping.Moreover, the bottom 11" in the body 13 of the element is seen. Theclamping ring 42 is provided with a calibration device 43 whichdetermines the thickness of the material, drawn anew, in the wall part18.

FIG. 12 shows an element body 50 which has been formed by means of thepress device 20a according to FIG. 9 and in which the edge part of theelement has been produced from the body. In FIG. 13, the shaping processof the body 50 was initiated with the aid of a device shown in FIG. 11.The shaping process has progressed to such an extent that a mainlycylindrical larger part, having the same diameter as the body 50, and ashorter part 59 have been formed. In FIG. 14, the shaping process hasbeen completed, a mainly cylindrical body 52 of the same diameter as inthe shorter part in FIG. 13 having been formed.

FIG. 15 shows a body 53, the shorter part 59 of which has been reshapedwith the aid of a device shown in FIG. 11 for the purpose of furtherreducing the diameter of the shorter part 59'. There is a transition 58between the shorter cylindrical part 59' and the larger part of the body53.

FIG. 16 shows a bottle-like container 70' produced from a body 53according to FIG. 15. The bottom part of the shorter part 59' has beensevered and replaced by a closure 55, for example a cap. The mouth edgesformed on severing the bottom part were expanded and beaded, after whichthe material in the beaded material zones has preferably been given anincreased crystallinity as a result of heating the material up to thecrystallization temperature. This gives additional strength at the mouthedge so that the latter is well suited for closing the container, forexample by means of a cap or a crown cork. The transition, alreadymentioned, between the shorter part and the larger part of the body nowforms a bottle neck 58'. The figure also shows how an end disc 56 isfixed at the other end of the container 70', after the container hasbeen filled. As a result of expanding, beading and heating of thematerial, material sections are here also obtained which are suitable,for example, for fitting an end disc by crimping, in order to close thecontainer.

FIGS. 17-19 show counterparts to FIGS. 12-14. The figures show how anelement body, formed from the body 11' according to FIG. 7, is subjectedto an axial lengthening, with simultaneous reduction in the diameter ofthe body, and forms an almost completely cylindrical body 61, the bottompart of this body consisting of a material section 62 of mainlyamorphous material. During the shaping process, an intermediate form ofthe body results, which is marked 60 in FIG. 18.

In the embodiment of the invention in which a body is formed whichcomprises an amorphous bottom section, a material zone is also obtainedwhich is suitable as a fixing material for welding on additional partsto the body. By rendering the material crystalline, a zone of extremedimensional stability is obtained, whereby it becomes possible to usethe container for storing liquids under pressure, for example beveragesto which carbonic acid has been added, without a risk of deforming thebottom part. The concept of the invention also comprises the replacementof the plane embodiment of the bottom part by a convex or concave face,depending on the particular wishes which apply corresponding to theindividual applications.

FIGS. 20-22 show optional embodiments of blow-moulded containers. Allthe containers are closed by end discs in the manner already describedin connection with FIG. 16. Of course, this combination of ablow-moulded container and an end disc is to be regarded only as anexample of the possibilities available for closure.

FIG. 20 shows an embodiment in which all the material in theblow-moulded container consists of material previously drawn. Thecontainer is formed from a body part either according to FIG. 12 oraccording to FIG. 14.

FIG. 21 shows an embodiment of a blow-moulded container which has beenformed from a body part according to FIG. 17 or FIG. 19. Onblow-moulding, the amorphous material zone 22 remained in the amorphousstate without change, and it represents a thicker section in the bottompart of the container. In certain embodiments, this section is heated upto the crystallisation temperature of the material in order to form abottom section which is particularly suitable for withstandingdeformation forces, for example, forces due to an internal pressure inthe container. The amorphous material is also suitable for the purposeof welding additional plastic parts thereto.

FIG. 22 shows an embodiment of a blow-moulded container which has beenformed from a body part, the bottom of the body part consistingalternately of material sections, which have been drawn until flow setsin, and of those material sections which have retained their originalthickness. In this way, a simple amorphous material section 21 has beenformed which is surrounded by an annular amorphous section 72 which islocated below the central section. The central section and the annularsection are connected by material which has been drawn until flow setsin. The annular material section thus forms standing surfaces for thecontainer. The parts forming the shell of the container are as a ruleshaped from redrawn material. At least in the cases where the containerhas a relatively large axial dimension, such redrawing is necessary.

Blow-moulding is carried out in any known manner at a temperature of thematerial, which is above the glass transition temperature Tg. Normally,blow-moulding takes place against heated mould walls. In certainillustrative embodiments, a heated elongate blow mandrel is required inorder to avoid excessive cooling of the material during theblow-moulding step.

The material oriented by flow possesses improved strength properties inthe direction of orienting, which is largely the same as the directionof drawing the material. Since the material has been heated to atemperature above the glass transition temperature Tg, there are nodifficulties in a blow-moulding process with regard to reshaping theelement by stretching the material in a direction which is mainly atright angles to the said direction of orienting. An element reshaped inthis way forms, for example, a container having a central shell surfaceof a diameter which exceeds the diameter of the opening, and having abottom which consists of a standing surface which represents thetransition between the lower edge of the shell surface and the bottomsurface, the bottom surface either being slightly concave or consistingof annular material sections which are displaced relative to one anotherin the axial direction of the container.

The above description merely represents examples for the application ofthe invention. The invention allows of course that a number ofcombinations of drawing steps take place, zones of drawn and undrawnmaterial also forming alternately. For example, the body consists ofwall parts with sections which contain undrawn material, whilst thebottom part consists of sections, for example annular sections, whichcontain undrawn material and which are displaced in the axial directionof the body relative to the lower edge of the wall part.

The concept of the invention comprises many optional embodiments.According to one of these, drawing until the material in the body of theelement flows is effected by a number of successive drawing steps, thecontact area of the press device decreasing for each drawing step. Theresult of this is that the width of the material zone 15 is adapted tothe extent to which the drawing step has proceeded.

We claim:
 1. A process for the manufacture of an article frompolyethylene terephthlate or similar materials comprising providing asubstantially flat blank of amorphous, polyethylene terephthlate havinga crystallinity of less than 10%, clamping said blank between clampingdevices to form at least one inner zone completely surrounded by aclosed, band-like, clamped section of material, applying a press elementagainst said inner zone over a region smaller than the total area ofsaid inner zone, whereby a second closed, band-like zone is formedbetween said clamped band-like section and said inner zone to which thepress element is applied, relatively displacing said press element andsaid clamping devices with the thermoplastic material at a temperaturebelow the glass transition temperature (Tg) while maintaining said presselement in contact with said inner zone, the second band-like zone beingsubstantially greater than the thickness of the blank whereby thematerial in said second band-like zone is freely stretched by drawing ina drawing region between the outer surface of the press element and theinner surface of the clamping devices without contact of the drawnmaterial with the surfaces of the clamping devices, the material in saiddrawing region forming a transition zone at which flow takes place inthe material reducing the original thickness of the blank by a factor ofabout 3 to effect crystallization thereof and monoaxial orientationwhereby a drawn element is formed which comprises an edge part composedof said clamped section and a body which is drawn relative to said edgepart and includes material drawn until it flows to form the monoaxiallyoriented crystallized material, the crystallinity of said material ofsaid body being between 10% and 25%, while the crystallinity of thematerial in said edge part and in any undrawn part of the body retainsits original value of less than 10%, and reshaping said body at atemperature above the glass transition temperature (Tg) by blow-mouldingto achieve the shape of the final product.
 2. A process as claimed inclaim 1, wherein the crystallinity of said blank is less than 5%.
 3. Aprocess as claimed in claim 2, wherein the crystallinity of the drawnmaterial is between 12 and 20%.
 4. A process as claimed in claim 1comprising heating the body during blow-moulding.
 5. A process asclaimed in claim 1 comprising elongating said body in the axialdirection before blow-moulding by a number of repeated drawing steps toretain reduced dimensions at right angles thereto, the thickness of thedrawn material being substantially unchanged.
 6. A process as claimed inclaim 1, wherein the drawing step for causing the material to flow iscontinued until approximately all of the material in the inner zone hasundergone flow, as a result of which approximately all of the materialin the body consists of material which has undergone flow.
 7. A processas claimed in claim 1, wherein the contact surface of the press elementwith said inner zone is such that it is completely surrounded by saidclosed, band-like, clamped section, in order to cause the flow of thematerial to start at the press element.
 8. A process as claimed in claim7, wherein the width of the clamped material is selected so that flow ofthe material at the end of the drawing step extends to said material andends thereat.
 9. A process as claimed in claim 8, wherein thetemperature of the material before drawing is room temperature.
 10. Aprocess as claimed in claim 8 comprising subjecting the material, atleast during the drawing step, to accelerated cooling in the flowregion.
 11. A process as claimed in claim 10 comprising cooling thepress element such that, on drawing the material, the regions in whichthe material flows are cooled.
 12. A process as claimed in claim 1further comprising severing said body from said edge part prior to saidreshaping of said body.